N Korea calls for peace treaty with US

North Korea has called for the conclusion of a peace treaty with the United States and a halt to US military exercises with South Korea to end its nuclear tests.

The isolated state has long sought a peace treaty with the United States, as well as an end to the exercises by South Korea and the United States, which has about 28,500 troops based in South Korea.

"Still valid are all proposals for preserving peace and stability on the peninsula and in Northeast Asia including the ones for ceasing our nuclear test and the conclusion of a peace treaty in return for US halt to joint military exercises," North Korea's official KCNA news agency cited a spokesman for the country's foreign ministry as saying early on Saturday.

Asked if the United States would consider a halt to joint exercises, US State Department spokesman John Kirby said it had alliance commitments to South Korea.

"We are going to continue to make sure the alliance is ready in all respects to act in defence of the South Korean people and the security of the peninsula," he told a regular news briefing.

Asked earlier this week about North Korea's call for a peace treaty, the State Department reiterated its position that it remained open to dialogue with North Korea but said "the onus is on North Korea to take meaningful actions toward denuclearisation and refrain from provocations".

The two Koreas remain in a technical state of war since their 1950-53 conflict ended in a truce, not a peace treaty.

North Korea said on January 6 it had tested a hydrogen bomb, provoking condemnation from its neighbours and the United States.

Experts have expressed doubt that the North's fourth nuclear test was of a hydrogen bomb, as the blast was roughly the same size as that from its previous test, of a less-powerful atomic bomb, in 2013.